One or more methods of geological and geophysical exploration and/or research are conducted in connection with oil and gas recovery, as well as other fields of subterranean exploration, research and/or production (such as mineral mining, earthquake monitoring, and geothermal heat extraction). At least one method of such exploration and/or research involves forming a borehole (or well bore) within a subterranean formation, and thereafter placing one or more sondes or sensor pods within the borehole. The borehole can be either vertical or horizontal. Conventional sondes or sensor pods employed in this manner are often configured to detect and/or collect seismic and/or acoustic signals while disposed within the borehole. Accordingly, many conventional sondes or sensor pods are further configured to be selectively stabilized or immobilized within the borehole in order to facilitate detection and/or collection of seismic and/or acoustic signals. In this manner, the sondes or sensor pods are often selectively positioned and repositioned at various depths or locations within the borehole. Various types of prior art sondes or sensor pods have been developed for detecting and/or collecting seismic, acoustic and/or other types of data within a borehole or well hole. Further, various types of prior art devices have been developed with the goal of selectively stabilizing or immobilizing such sondes or sensor pods within the borehole. However, certain shortfalls can be associated with such prior art sondes and/or sensor pods, and devices for stabilizing the same within boreholes.
More specifically, it is desirable to form a firm and secure connection between the sensing units (contained within the sondes and/or sensor pods) and the wall of the borehole so that positive mechanical and acoustical coupling occurs. Such positive mechanical and acoustical coupling of the sensor support units (i.e., the sondes and/or sensor pods) with the borehole wall improves the quality of the signal received by the sensing unit, and also reduces the opportunity for miscellaneous noise to be introduced (which can result from movement between the borehole wall and the sonde and/or sensor pod). Thus, the clamping force exerted between the borehole wall, and each sonde and/or sensor pod in an array of such devices, is significant in contributing to the overall quality of data collected by the array.
Further, it is not only desirable that each sonde and/or sensor pod within a receiver array be able to establish a firm and secure connection to the borehole wall during a data collection period, but it is also desirable that each sonde and/or sensor pod within a receiver array be able to affirmatively decouple from the borehole wall so that the receiver array may be easily repositioned within, or withdrawn from, the borehole. Many prior art devices provide for forming a secure physical (and thus, acoustical) connection between a sonde and/or sensor pod and a borehole wall. However, these devices do not allow for the sonde and/or sensor pod to be affirmatively withdrawn (or retracted) from contact with the borehole wall following data collection. This is particularly problematic when the sondes/pods are to be repositioned within, or withdrawn from, the borehole. Specifically, it is desirable that: (i) individual sondes/pods do not become stuck against the borehole wall when the receiver array is to be (a) further lowered within the borehole after an initial set of readings are taken from the sensors in the receiver array, or (b) withdrawn from the borehole following data recording; and (ii) individual sondes/pods do not abrade against the borehole wall when the receiver array is being withdrawn from the borehole. In the latter situation (i.e., sondes/pods abrading against the borehole wall while the receiver array is being withdrawn from the borehole), such abrasion can produce the following deleterious effects. In the first instance, if the outer wall of the sonde/pod is roughened by such abrasion, then the mechanical and acoustical coupling between the outer wall of the sonde/pod and the borehole wall will likely be reduced, thus resulting in lower quality of data received by the sensors within the well sonde/pod. In the second instance, if the thickness of the outer wall of the sonde/pod is reduced by such abrasion, then the initial calibration of the data quality and vector fidelity recorded by the sensor will change thus affecting the quality of the measurements taken by the sensors in the sonde/pod.
As can be appreciated, the problems described above are significant even for a single sonde/sensor placed within a borehole, but become more acute then encountered within a receiver array comprising a plurality of sondes and/or sensor pods.
It is thus desirable to provide for an array of sondes/pods, which are to be deployed in a downhole subterranean formation, which: (i) allows for a positive mechanical and acoustical connection of each sonde/pod in the array with the borehole wall formed in the subterranean formation; and (ii) also allows for each sonde/pod in the array to be affirmatively withdrawn from contact with the borehole wall (as selectively desired) so that the array of sondes/pods can be moved within the borehole (i.e., relocated within, or withdrawn from, the borehole) without the borehole wall degrading the physically integrity of the sondes/pods, and consequently affecting (i.e., degrading) the quality of signals received by sensors within the sondes/pods. It is further desirable to provide for a mechanism which not only achieves the desired positive mechanical and acoustical connection of each sonde/pod in the array with the borehole wall, but further (and subsequently) achieves the removal (in a positive manner) of each sonde/pod in the array from contact with the borehole wall. It is furthermore desirable that the borehole seismic array can be deployed without the use of expensive borehole tractors in both vertical and horizontal boreholes.